How do I add or remove people from a group text message?
To add a contact to an existing group text message follow these steps in Messages:
- Open the group message thread
- Tap the information icon (the letter "i" with a circle around it) the upper right corner
- Tap Add Contact to add another party to the group message
UPDATE: You can now delete a person who you added to a group message by going to the "Details" panel and swiping on their name. Learn more about adding and removing contacts with iOS here.